Summary Exercise robustly enhances cognitive performance across the lifespan but the mechanisms are not well understood. The long-term goal of this research program is to elucidate the neurological mechanisms by which exercise improves cognition. The objective of this application is to determine the origin of exercise-induced hippocampal neurogenesis and enhanced behavioral performance, whether from contracting muscles or acute activation of the hippocampus during physical exertion. Recent work has emphasized the importance of the muscle-brain axis and has assumed the main signals originate from skeletal muscle. On the other hand, there is a large and well established literature illustrating a close correlation between neural activation of the hippocampus and the speed of movement. Results will provide crucial information for deciding whether to focus on the muscle secretome or mechanisms within the brain for recapitulating pro-cognitive effects of exercise. The rationale is to develop better strategies for neuronal regeneration and repair and for ameliorating cognitive deficits associated with neurological disorders. The central hypothesis is that both muscle contractions and hippocampal neuronal activation each independently enhance neurogenesis and related behaviors. The hypothesis is supported by preliminary studies showing that both repeated electrical contractions of the hindlimb muscles and activation of hippocampal neurons increases hippocampal neurogenesis in mice. One of the PIs has a productive research program on exercise induced-neurogenesis and measuring behavioral performance in mice, and the other has expertise on muscle physiology and electrical stimulation. Moreover, the PIs have developed multiple innovative methods for powerful hypothesis testing. The objectives of this application will be accomplished by pursuing 2 specific aims: 1) Determine the extent to which repeated electrical contraction of the hindlimb muscles is sufficient to increase adult hippocampal neurogenesis and enhance learning and memory. 2) Determine the extent to which optogenetic activation of the dentate gyrus in a pattern that mimics running is sufficient for exercise-induced neurogenesis and enhanced behavioral performance. An established procedure for electrically contracting the hindlimb muscles will be used to repeatedly contract the muscles while the mouse is anesthetized. State-of-the-art optogenetic methods will be used to instantaneously activate dentate gyrus granule neurons that were acutely and transiently activated in response to running and to measure the long-term effects on neurogenesis and behavior. Elucidating and unequivocally establishing mechanisms underlying pro-cognitive effects of exercise holds the key to discover novel and more efficient ways to maintain, promote and improve cognitive performance. The proposed research is highly innovative, it addresses pressing questions in the field using very novel strategies and state-of-art optogenetics technology that will allow us to generate causal, mechanistic data on the origin of exercise's effects on neurogenesis and cognitive performance.